Electric ignition system and sparking plug for internal combustion engines



- W. B. SMITS AND SPARKING PLUG FOR INTERNAL COMBUSTION ENGINES July 26,1938.

ELECTRIC IGNITION SYSTEM Filed Oct. 19, 1936 INVENT R {;&e 8 e/ Ma /4754Patented July 26, 1938' PATENT OFFICE ELECTRIC IGNITION SYSTEM ANDSPARK- ING PLUG FOR INTERNAL COMBUSTION ENGINES Wytze Beye Smits,Kassel-Wilhelmshohe,

; Germany -Application October 19, 1936, Serial No. 106,431 In GermanyOctober 18, 1935 10 Claims.

(Granted under the provisions 01' sec. 14, act of March 2, 192']; 357 O.G. 5)

This invention relates to ignition systems for internal combustionengines and has as a primary object the provision of a system utilizinga condenser charged with a current of relatively low tension and whichis discharged directly across the electrodes of the sparking plugs.

A further object is to provide in a system of this character an ignitioncircuit arrangement including a condenser alternately charged anddischarged directly across the electrodes of a sparking plug.

A further object is the provision of an ignition system for internalcombustion engines by which the operating current employed may be ofmaterially lower tension than is the tension of current conventionallyemployed in the firing of known types of sparking plugs as utilized inthe art prior to the advent of this invention.

Other objects will be apparent from the description.

Developments of recent years have led to a constant increase in engineemciency combined with a saving in petrol. This goal has been attainedby means of a constant increase of the pre-compression pressure, but alimit has been set on this development by the sparking plug. At a highcompression pressure there results also a high temperature. At thesehigh temperatures the internal surface leakage paths of the high tensioninsulators must be kept small, whereby on the other hand they arerendered very sensitive to oil.

The plugs must for a determined engine always be able to attain acertain self-cleaning temperature in order that the surface leakagepaths of the high tension insulators can be burnt free from soot andother residues of combustion. This principle has made necessary thelarge number of types of sparking plugs which the plug manufacturershave to market at the present tin e. A new engine of one and the samemanufacture requires various types of plugs in accordance with whetherthe engine is new or has been run in or whether it has already covered arelatively large distance. From this results the following law, based onexperience: A plug with a high intensity of incandescence is extremelysensitive to oil. A plug which is very insensitive to oil has acorrespondingly low intensity of incandescence. As a result of these twocharacteristics a limit is now set to the present development ofhigh-compression engines, since the one characteristic excludes theother.

Turning briefly to the electric ignition itself, it may be said that aninfinite number of tests have shown that the most favorable tension isone of 15,000 to 20,000 volts. It may be mentioned in this connectionthat in the change-over from magneto to battery ignition which hasoccurred in the course of the years the voltage itself has not beenmaterially changed.

These relatively high tensions have been required in order at theconsiderable pressures which were necessary in the precompressed statein the cylinder to be able to bridge the electrode gap by a spark.

The employment of such a high tension in the region of 20,000 volts has,however, resulted in difficulties with the introduction of the insulatedmiddle pole in a sparking plug, since it must be borne in mind also thatthe sparidng plug itself must be brought to fairly high temperatures inorder that the insulation of the centre electrode may constantly burnfree oi rust and carbon, in order thereby to maintain the maximuminsula= tion of the centre pole. If these self oieaning temperatures arenot reached, soot, carbon, gradually collects on the plug insulator,whereby a carbon connection between the centre pole and the externalwall comes into existence, which then leads to the plug failing tospark.

The object or" the present application is an igni-= tion system whichallows of these high voltages being materially dispensed with, wherebythe insensitiveness of the plugs to being hindered in their working byoil or soot is very considerably increased.

The principal characteristic of the invention is the employment of acondenser which is charged with a current of relatively low tension andwhich is discharged directly across the electrodes of a sparking plugwith a very narrow electrode gap.

This charging and discharging of the condenser is effected in anysuitable manner and the current distribution to the sparking plug iscontrolled by suitable timing means such as, for example, a

commutator. This commutator assures the con trol of the ignition spark.

The advantage of an ignition system characterized as above describedlies, above all, in a special energetic ignition of the inflammablemixture, whereby a better utilization of the fuel is guaranteed.Further, as has been indicated above, such a sparking plug actuated bycondenser discharges is extremely insensitive to disturbance by oil,since also such a sparking plug with a condenser ignition always worksperfectly, and must work perfectly in comparison to the high tensionignition employed hitherto, since with such a condenser ignitionconsiderably lower tensions are employed.

Regarding the matter closely, it will be seen that carbon is the enemyof the present sparking plugs, while carbon particles with this newignition system facilitate the discharge of the condenser and thusreliability is guaranteed under all possible working conditions.

The above described electric ignition system utilizes for ignition aquantity of low tension current which is stored up in a condenser.

An additional object of the present invention is an extension of theapplication of the system to engines running at high speeds. It is usualwith such engines for use in racing cars and airplanes which areequipped with high tension ignition of approximately 30,000 volts to fita double igniter in order to obtain perfect and powerful ignitions evenat the highest rotation speeds. The avoidance in all circumstances ofthese costly double equipments when the invention is put into employmentwith low tension ignition of about 1,000 volts is an object of thepresent invention.

A further characteristic feature therefore resides in the fact that theabove mentioned condenser as well as being discharged is also chargedacross the electrodes of the plug and thus in both cases produces aspark which institutes an ignition and respectively combustion. Itresults from this that the control mechanism requires to work at onlyone-half the number of revolutions which-apart from saving a costlydouble ignition installation-guarantees a considerably longer life andmaximum certainty in working.

Figures 1 and 2 illustrate schematic arrangements of electric ignitionsystems for internal combustion engines as arranged in accordance withthe invention.

Now the sparking plug systems employed for ignition at the present timeare all founded upon the principle of high-tension ignition. With thisit is necessary that the more central pole should be insulated from theother pole by a good heatresisting insulation with high insulatingefficiency. The better this insulation is and remains, up to theelectrode gaps, the more certain will such a sparking plug ignite.

In practical working there are many difficulties associated with thesesparking plugs actuated by high tension. If we consider a sparking plugwhich has a high intensity of incandescence, we find that the projectingpart of the insulation mass in the combustion chamber is very short; inthe case of such a sparking plug with a small insulator and consequentlyshort surface leakage path the vulnerability to disturbance by oil andsoot is therefore very great. If, on the other hand, we consider asparking plug offering good resistance to disturbance by soot and oil,we find that the insulation part which projects in the combustionchamber is very large. With this the surface leakage path is long and byreason of this the plug is less vulnerable to interference by oil andsoot, but to balance this, the intensity of incandescence is lower. Atthe present day the limit of possibilities has been reached in thisdevelopment. The present invention overcomes these difficulties (1)Because electric tensions of 20,000 volts are no longer employed,considerably lower tensions being used instead;

(2) Because these tensions are not led direct to the sparking plug; theyare led indirectly over a condenser which discharges at the moment atwhich a charged condenser is connected to the sparking plug.

In order to obtain a proper transmission of this discharge to thesparking plug, the sparking plug must be so constructed that thedistance between the electrodes is so small and the electrodes are sothick that the particles of oil, etc. which are deposited are notcompletely burnt off, for it is precisely these particles which form ameans of assisting the condenser discharges. There exist twopossibilities of successfully carrying through these procedures with asparking plug.

(1) As described above;

(2) By making the insulation layer between the sparking plug poles sothin and the heat conduction from this place so great that the particlesof oil and soot in question can easily deposit themselves on this layerand thereby greatly facilitate the condenser discharges.

By means of this manner of construction it is possible for the sparkingplugs to have a high intensity of incandescence and at the same time tobe extremely intensive to oil and soot, since it is precisely theparticles of oil and carbon, and respectively the soot, which increasethe operating efficiency of the sparking plug.

In the schematic Figs. 1 and 2, A designates the source of condensercharging current, B the changing switch, C is the condenser, D thesparking plug and E the ignition place.

Ignition systems are known in which a magneto charges a condenser whichis subsequently discharged through the primary winding of an inductioncoil thus producing at each ignition a series of small sparks, that isto say, a high frequency spark. The present invention differentiatesfrom such known systems by the fact that the condenser is charged anddischarged directly across the electrodes of a spark plug producingthereby intense sparks and with the employment of only a relatively lowvoltage.

I claim:

1. Electric ignition system with direct discharging of a condenseracross an ignition point, characterized in that the condenser is chargedwith a current having a voltage of the order of about 1,000 volts and isdischarged across the electrodes of a sparking plug having a spark-gapwidth of the order of 0.3 mm. or less.

2. Electric ignition system according to claim 1, characterized in thatthe condenser is alternately charged and discharged across theelectrodes of the sparking plug.

3. Electric ignition system according to claim 1, characterized in thatthe charging and discharging of the condenser is controlled by suitabletiming means.

4. Electric ignition system with direct discharge of a condenser over asparking distance characterized by that the condenser, free from everyadditional cooperating apparatus is charged by a low-tension current ofabout 1,000 volts or below and discharged over the electrodes of a sparkplug, the air distance whereof is about 0.3 mm. or below so thatcombustion residues may be deposed there which favorize the condenserdis charge.

5. Electric ignition system according to claim 1, characterized in thatthe condenser is alternatively charged and then discharged over the veryreduced insulation layer separating the ignition poles of a spark plugand whereupon combustion residues may be disposed.

6. Electric ignition system characterized in that it comprises acondenser exclusively charged by low-tension (about 1,000 volts or less)without any additional cooperating apparatus and at the dischargewhereof only very short ignition distances (0.3 mm. or less) shall bebridged.

'7. In an electric spark plug ignition system composed of an ignitioncircuit and a condenser, the combination of only a low tension chargedand discharged condenser of the order of about 1,000 volts with sparkplug electrodes having a spark gap width of the order of less than 0.3mm.

8. An ignition system for internal combustion engines, consisting of aspark plug, a condenser, a current source, and means for alternatelycharging and discharging the condenser from said current source directlyacross the spark plug terminals as the sole spark producing meanstherefor.

9. An ignition system for internal combustion engines, consisting of aspark plug terminal gap of less than 1 mm., a condenser, a currentsource of 1,000 volts or less, and means for alternately charging anddischarging the condenser from said current source directly across thespark plug terminals as the sole spark producing means therefor.

10. An ignition system for internal combustion engines, comprising incombination, a low voltage current circuit, a condenser receiving acharge therefrom, a spark plug, and means for discharging the condenserdirectly across the plug terminals as the sole spark producing meanstherefor. 7

WYTZE BEYE SMITS.

